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JavaScript ReferenceError – Invalid assignment left-hand side
  • Last Updated : 24 Jul, 2020

Basic Example of ReferenceError – Invalid assignment left-hand side, run the code and check the console

Example:

Javascript




<script>
    if (Math.PI = 10 || Math.PI = 5) { 
        document.write("Inside Loop");
    }
</script>

Output:

ReferenceError: Invalid left-hand side in assignment

This JavaScript exception invalid assignment left-hand side occurs if there is a wrong assignment somewhere in code. A single “=” sign instead of “==” or “===” is an Invalid assignment.

Message:



ReferenceError: invalid assignment left-hand side

Error Type:

ReferenceError

Cause of the error: There may be a misunderstanding between the assignment operator and a comparison operator.

Example 1: In this example, “=” operator is misused as “==”, So the error occurred.

HTML




<!DOCTYPE html>
<html>
    <head> </head>
    <body style="text-align: center;">
        <h1 style="color: green;">
            GeeksforGeeks
        </h1>
        <p>
            JavaScript ReferenceError - 
            Invalid assignment left-hand side
        </p>
  
        <button onclick="Geeks();">
            click here
        </button>
        <p id="GFG_DOWN"></p>
  
        <script>
            var el_down = document.getElementById("GFG_DOWN");
            function Geeks() {
                try {
                    if ((Math.PI = 10 || Math.PI = 5)) {
                        document.write("Inside Loop");
                    }
                    el_down.innerHTML = 
                      "'Invalid assignment left-hand side'" + 
                      " error has not occurred";
                } catch (e) {
                    el_down.innerHTML = 
                      "'Invalid assignment left-hand side'" + 
                      "error has occurred";
                }
            }
        </script>
    </body>
</html>

Output:

Example 2: In this example, the + operator is used with the declaration, So the error has not occurred.

HTML




<!DOCTYPE HTML>
<html>  
<head>     
</head>   
<body style="text-align:center;"
    <h1 style="color:green;">  
        GeeksforGeeks  
    </h1
    <p>
        JavaScript ReferenceError -
        Invalid assignment left-hand side
    </p>
     
    <button onclick = "Geeks();">
        click here
    </button>
    <p id="GFG_DOWN"
    </p>
         
    <script
        var el_down = document.getElementById("GFG_DOWN");
        function Geeks() { 
            try {
                var str = 'Hello, '
                + 'Geeks'; // Error Here
                el_down.innerHTML = 
                "'Invalid assignment left-hand side'"+
                "error has not occurred";
            } catch(e) {
                el_down.innerHTML = 
                "'Invalid assignment left-hand side'"+
                "error has occurred";
            }
        
    </script
</body>   
</html>

Output: 

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